Warning, enabling your root account might pose extra security threads. If you don't care, read on :)
When you want to use the root account via su -, but you are getting this message it might mean that the shell is wrong in /etc/passwd. You'll get the following symptons
[vi-admin@vad ~]$ sudo su
This account is currently not available.
You can fix this by using the sudo vi /etc/passwd . You should fix the root line by changing the shell from /sbin/nologin to /bin/bash. for example
Save the file and you should be able to login.